Abstract P3-07-11: Avoidance of axillary lymph node dissection in patients with 1-2 pre-operative positive lymph nodes undergoing upfront surgery: ‘Primary targeted axillary dissection’ early outcomes

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Abstract Introduction: NCCN guidelines support safe omission of axillary lymph node dissection (ALND) in clinically node negative (cN0) patients with 1-2 positive sentinel lymph nodes (SLNs) if they meet the eligibility criteria of ACOSOG Z0011 and AMAROS trials. For patients undergoing neoadjuvant systemic anti-cancer therapy (SACT), targeted axillary dissection (TAD) is recognised as a highly accurate technique to spare patients ALND whose cN+ status converts to ypN0. However, there is no consensus on the optimal management of patients with low volume cN+ disease undergoing upfront surgery with ASCO guidelines recommending ALND and NCCN guidelines supporting primary TAD. In this context, ‘primary TAD’ combines these principles to de-escalate axillary surgery in patients with ultrasound-detected abnormal or biopsy-proven 1-2 positive lymph nodes (cN1) that are clipped for removal in combination with SLN biopsy to optimise further axillary surgical decisions. This method evolved after biopsy-proven involved nodes were missed during planned ALND. Aims: To evaluate the early outcomes of primary TAD in a single high volume tertiary cancer unit in the United Kingdom (UK). Methods: A prospective database of the first 126 patients ≥ 18 years with cT1-2cN1 undergoing primary breast surgery either as breast conserving surgery or mastectomy with primary TAD between 30/08/2018 and 12/03/2024 at the Royal Marsden NHS Foundation Trust was evaluated. We define primary TAD as removal of 1-2 marked axillary nodes using Magseed, either biopsy-proven or suspicious on axillary ultrasound scan but indeterminate biopsy, combined with SLN mapping with the use of Tc99m / SPIO / Patent Blue V. The clipped node(s) were sent to histopathology (as already known to contain disease), and additional SLNs underwent intra-operative assessment using one step nucleic acid (OSNA). If a total of 3 positive nodes (including marked nodes + those with macrometastasis on OSNA) were confirmed, the patient underwent completion ALND in the same operative sitting. If only 1-2 nodes, total from marked nodes and OSNA, contained macrometastatic disease, the patient was spared ALND and offered regional nodal irradiation (RNI). Patient demographics, tumor characteristics, treatment details and outcomes including breast and/or axillary recurrence, distant recurrence and overall survival were assessed. Descriptive statistics were used to report results. Results: A total of 125 women and 1 man underwent primary TAD. The median age at surgery was 60.5 years. The majority of tumors (109/126) were hormone positive (HR+) and HER2 negative (86.5%), with 78/126 of the luminal A subtype (61.9%) and cT2 with a median tumor size of 24mm (IQR 17-34.8). Pre-operatively, 24/126 (19%) had suspicious nodes unproven on biopsy, 1 abnormal and proven axillary metastatic node was detected in 74/126 (58.7%), and 2 abnormal with 1 biopsy-proven node in 28/126 (22.3%). Clipped node(s) were successfully removed in 125 patients. A median of 3 non-Magseed SLNs were excised for OSNA, of which median 0 (IQR 0-1) were positive. Of 126 patients, 121 (96%) had axillary metastatic Magseed node(s), 97 (77%) avoided ALND, 27 (21.4%) underwent immediate ALND, 2 (1.6%) underwent delayed ALND post SACT. Out of 126, 65 (51.6%) patients underwent RNI. Median follow-up was 21.2 months (IQR 11.2- 35.8); 1 patient developed axillary recurrence requiring further axillary surgery, no patients developed breast recurrence, and 3 patients developed and died of distant metastasis. Conclusion: Primary TAD is feasible with reassuring early oncological outcomes but long-term follow-up is required. This method can be utilised to optimise axillary surgery in suitable patients to safely facilitate omission of routine ALND. Citation Format: Radhika A Merh, Jennifer Rusby, Marios Konstantinos Tasoulis, Katherine Krupa, Rachel O'Connell, Gerald Gui, William Allum, Victoria Sinnett, Julie Scudder, Peter Barry. Avoidance of axillary lymph node dissection in patients with 1-2 pre-operative positive lymph nodes undergoing upfront surgery: ‘Primary targeted axillary dissection’ early outcomes [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P3-07-11.

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